Inducibility of atrial fibrillation during atrioventricular pacing with varying intervals: Role of atrial electrophysiology and the autonomic nervoussystem

Pacing and Atrial Electrophysiology. Introduction: Patients receiving VVI p acemakers have a higher incidence of paroxysmal atrial fibrillation (AF) th an those receiving DDD pacemakers. However, the mechanism behind the differ ence is not clear. The purpose of this study was to investigate whether atr ial electrophysiology and the autonomic nervous system play a role in the o ccurrence of AF during AV pacing. Methods and Results: The study population consisted of 28 patients who had (group I, n = 15) or did not have (group II, n = 13) AF induced by a single extrastimulus during pacing with different AV intervals. Atrial pressure, atrial size, atrial effective refractory periods, and atrial dispersion wer e evaluated during pacing with different AV intervals. Twenty-four-hour hea rt rate variability and baroreflex sensitivity also were examined. Atrial p ressure, atrial size, effective refractory periods in the right posterolate ral atrium and distal coronary sinus, and atrial dispersion increased as th e AV interval shortened from 160 to 0 msec. During AV pacing, group I patie nts had greater minimal (52 +/- 17 vs 25 +/- 7 msec; P < 0.005) and maximal (76 +/- 16 vs 36 +/- 9 msec; P < 0.005) atrial dispersion than group II pa tients. The differences in atrial size and atrial dispersion among differen t AV intervals were greater in patients with AF than in those without AF. B aroreflex sensitivity (6.6 +/- 1.7 vs 3.9 +/- 1.0; P < 0.00005), but not he art rate variability, was higher in patients with AF than in those without AF. Conclusion: Abnormal atrial electrophysiology and higher vagal reflex activ ity can play important roles in the genesis of AF in patients receiving pac emakers.